1. Field of the Invention
The present invention relates generally to object targeting and more particularly to a device or system and its associated method for performing closed-loop tracking of laser rangefinder/designator returns and for using the laser rangefinder/designator returns as an illumination source for active imaging with the use of fluorescent conversion materials.
2. Background Information
Traditionally, military systems have used primarily 1.064 xcexcm wavelength Nd:YAG lasers for target designation and precision guided weapon delivery. In recent years, these designator lasers have been designed to also produce laser output at 1.5 xcexcm wavelength to provide a range-finding capability at an eyesafe wavelength.
By comparison, sensors most often employed to detect, identify, and select targets to be ranged and/or designated are based on a thermal imaging principle and are sensitive to radiation in the long-wave infrared (LWIR) waveband (7-12 xcexcm) or, more recently, in the mid-wave infrared (MWIR) waveband (3-5 xcexcm) waveband. Such imaging sensors are typically referred to in the art as forward looking infrared (FLIR) sensors.
In order for a FLIR sensor system to perform effectively, a laser must be able to immediately point at an object that has been identified by the sensor system. Thus, the accuracy of sensor systems is dependent on boresight accuracy between the lasers and imaging sensors, but such accuracy is presently limited by the ability to align and to maintain alignment between these devices. Alignment is usually achieved with the use of a boresight module assembly, where alignment accuracy is effected by such factors as mechanical tolerances and servo, tracker, and measurement errors. These factors have led to the design and use of very expensive boresight module assemblies requiring tight manufacturing tolerances. However, boresight accuracy in these assemblies is difficult to maintain, especially through extended use in operational environments that can produce very harsh thermal, shock, and vibrational conditions.
Attempts to provide closed loop tracking of a laser spot and/or active illumination for enhanced target recognition capabilities have followed one of two paths. The first involves the use of a FLIR sensor system with an additional sensor, such as a laser spot tracker (LST) or an active illumination near-IR imaging sensor (AITV). For example, U.S. Pat. No. 4,497,065 (Tisdale et al.), hereby incorporated by reference in its entirety, describes a system that includes both a passive sensor and an active sensor that is tuned to a predetermined laser wavelength. While these additional devices are sensitive to commonly-used laser wavelengths and can provide closed loop tracking and active illumination capability, their addition still requires a boresighting process. That is, a LST or an AITV needs to be boresighted to the FLIR sensor because, for example, the ability of either device to detect targets at night or in bad weather will be considerably poorer than that of a FLIR sensor. Therefore, accuracy problems as described above are not adequately addressed. This construction also requires the inclusion of associated optical path elements, support electronics, and power/cooling components. In short, the addition of a LST or an AITV for closed loop tracking and/or active illumination invariably results in an increase in total system cost, weight, and life cycle cost (e.g., more spare components required), while reducing the system reliability.
The other technique used involves using a FLIR sensor system with a focal plane array that is inherently sensitive to laser wavelengths. While effective in principle, this drastically reduces the focal plane array trade space available to system designers and often results in trade-offs that reduce system performance in other areas. In addition, focal plane arrays that are sensitive to both near-IR lasers and either the MWIR or LWIR FLIR bands are much more expensive than detector arrays sensitive only in either the MWIR or LWIR bands.
Finally, another factor that should be taken into consideration when designing a passive imaging sensor to be sensitive to common military Nd:YAG wavelengths is the proliferation of lasers in the modem battlefield with extremely high power output for use as directed energy weapons (DEWs). If a passive imaging detector array is sensitive to the Nd:YAG wavelength, it will also be susceptible to blinding or damage if illuminated by one of these DEWs.
It would be desirable to perform a closed-loop track of a laser spot on an object with a passive imaging sensor to allow a positive feedback to an operator of the laser pointing accuracy, and to use a laser rangefinder/designator as an illuminator for active imaging of potential targets.
Accordingly, the present invention is directed to a method of performing closed-loop tracking of laser rangefinder/designator returns and of using them as an illumination source for active imaging through the use of fluorescent conversion materials when an imaging array detector is not sensitive to the laser wavelength.
According to an exemplary embodiment of the present invention, a method for targeting is provided, including the steps of (i) illuminating an object with an energy, thereby creating a reflected energy of a first wavelength, (ii) receiving the reflected energy, (iii) converting the reflected energy into an energy of a second wavelength by fluorescent or phosphorescent conversion, and (iv) detecting the energy of a second wavelength.
According to another embodiment, a system for targeting is provided, including a convertor having a first side constructed to receive energy of a first wavelength and to convert the energy of a first wavelength into an energy of a second wavelength, and a distinct second side transmitting the energy of the second wavelength, the convertor comprising a fluorescent or phosphorescent material, and a sensor constructed to detect the energy of a second wavelength.